1. Field of the Invention
The present invention relates in general to continuously variable transmissions, and more particularly to the transmissions of a traction roller type which has paired motion transmitting traction rollers disposed between, and in engagement with, opposite toroidal input and output discs.
2. Description of the Prior Art
Hitherto, various types of continuously variable transmissions have been proposed and put into practical use particularly in the field of motor vehicles. Some of them are of a so-called traction roller type which comprises paired motion transmitting traction rollers disposed between, and in engagement with, opposite toroidal discs mounted on input and output shafts.
Under operation of the transmission, the torque applied to the input toroidal disc from a prime mover (that is, engine) is transmitted through the traction rollers to the output toroidal disc.
During this, the rotation speed change ratio between the input and output discs is infinitely varied depending on the angle at which each traction roller inclines relative to a common axis on which the input and output discs are mounted.
One transmission of such traction roller type is disclosed in Japanese Patent First Provisional Publication No. 62-127555. In this transmission, there are employed both a first biasing mechanism which biases the input and output discs toward each other in accordance with a torque applied to the input disc and a second biasing mechanism which biases the discs toward each other with a constant force. The first biasing mechanism comprises a loading cam structure which is constructed to shift the input disc toward the output disc upon generation of relative rotation between the input shaft (viz., a cam flange secured thereto) and the input disc. While, the second biasing mechanism comprises a pre-loaded spring which is compressed between the input disc and the input shaft (viz., the cam flange) through a spring seat.
However, the transmission of the publication has the following drawback due to the inherent construction of the second biasing mechanism.
That is, due to provision of the pre-loaded spring between the input shaft and the input disc, the relative rotation therebetween, which is required for operating the first biasing mechanism, is affected. In fact, the biasing force produced by the pre-loaded spring causes creation of a significant friction resistance against the relative rotation. This phenomenon tends to retard accomplishment of a locked condition between the input shaft (viz., the cam flange) and the input disc and thus deteriorates the performance of the first biasing mechanism and thus that of the transmission.